That's the exact problem.
I haven't tried the 'pressing messages tab' thing, maybe next time I log in.
On the start page (threads on left gallery pic on right) click and hold the dividing line between the two and drag the gallery pic out of the way, the subjects are underneath the gallery window, as if you were re-sizing the different panes.
Can you do a screen shot of the before and after of you clicking the line and having to drag the frame please.
Also, can you check to see it works any differently if you start off at http://www.tehforum.co.uk/forum/start.php?webtag=DEFAULT (so you have no navigation (start | messages | etc) and no top frame.
Okay, I have no idea why that is happening and I can't get it to happen here, I always get the main frameset reloading.
None the less I have fiddled a little bit, if you'd be so kind as to try again.